Comparison of ATH and SiO2 fillers filled silicone rubber composites for HTV insulators

To enhance the electrical and mechanical properties of silicone rubber (SIR) in the field of high-voltage insulation, conventional fillers such as aluminum hydroxide (ATH), fumed silica and precipitated silica have been used for many years. In this work, SIR composites filled with ATH, irregular SiO2 (IS) and sphere SiO2 (SS) were prepared by mechanical blending, and the effects of filler type and filler shape on mechanical, electrical and thermal properties of SIR composites were systematically investigated. Compared with ATH-SIR composites, SS-SIR composite exhibited better electrical and mechanical properties. It showed that the tensile strength of SS-SIR composites was up to 6.6 MPa, which was nearly 2-folded compared to ATH-SIR composite. According to the loss tangent results in combination with tensile fracture surface observation, the interfacial interaction between SiO2 fillers and SIR is stronger than that between ATH and SIR, and the dispersion is better in SiO2 fillers filled SIR composites than that in ATH filled composite. The breakdown strength of ATH-SIR composite is only 18.9 kV mm−1, while those of IS-SIR and SS-SIR composites are 24.9 and 24.8 kV mm−1, respectively. Among the three SIR composites, SS-SIR composite has lowest dielectric permittivity and dielectric loss. Compared with ATH-SIR composite, the SiO2 fillers filled SIR composites have the lower thermal conductivity ranging from 30 °C to 150 °C, but they exhibit the better arc aging resistance due to the good thermal stability and thermal conducting property at high temperature. Moreover, the SS-SIR composite exhibits the better arc aging resistance than IS-SIR composite.